MOSCOW (Reuters) - The head of Russia's dominant church urged its citizens to adopt children, speaking in a Russian Orthodox Christmas address on Monday after President Vladimir Putin signed a controversial law barring Americans from adopting Russian children.

Patriarch Kirill paid particular attention to the issue in a Christmas message, lending support to Putin's promises - issued along with a law that outraged liberals and child rights activists - that Russia will take care of its own.

"It is very important for our people to adopt orphans into their families, with joy and a special sense of gratitude to God, giving them not only shelter and an upbringing but also giving them their love," the Russian Orthodox Church head said.

The ban on American adoptions is part of a law Putin signed on December 28 in retaliation for U.S. legislation designed to punish Russian human rights violators, which the Kremlin chief said is poisoning relations.

Critics of the Russian legislation say Putin has held the welfare of children trapped in a crowded and troubled orphanage system hostage to political manoeuvring, reducing their chances of finding loving homes or adequate medical care.

The numbers of adoptions by Russian families are modest, with some 7,400 adoptions in 2011 compared with 3,400 adoptions of Russian children by families abroad - nearly 1,000 of those by Americans.

In signing the legislation, Putin echoed Russian lawmakers' arguments that American parents who have been accused of abusing their adopted Russian-born children have been treated too leniently by U.S. courts and law enforcement.

He also signed a decree ordering improvements in the care for orphaned Russian children and appealed to patriotism, suggesting that Russians have an obligation to care for the country's disadvantaged children.

Kirill added a religious element to that message, saying that "the Lord tells His followers that if they want to reach the Kingdom of God they must ... share their opportunities with the needy - primarily invalids, the elderly, and children."

"'Let the children come to me, and do not hinder them,' says the Lord. These words from Him should ... make us all realize how important children are in the eyes of God," he said.

"And as we celebrate Christmas I would like to appeal to everyone with a request: If you can take this important step in life aimed at adopting children, supporting orphans, take this step," Kirill said. "There should be no orphans in our country."

More than 650,000 children are considered orphans in Russia, including those rejected by their living parents or taken from dysfunctional homes. Of that total, 110,000 lived in state institutions in 2011, according to government figures.

More than three-quarters of Russians consider themselves Russian Orthodox, but far fewer attend church regularly despite a resurgence of religion following the demise of the communist Soviet Union.

The Russian Orthodox Church uses the Julian calendar and celebrates Christmas on January 7.

Kirill's midnight service at Moscow's Christ the Saviour Cathedral was shown live on state television, which also showed Putin - a former KGB officer who has cultivated close ties with the church - attending a service in the southern city of Sochi.

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